CN1837083A

CN1837083A - Wastewater treatment equipment

Info

Publication number: CN1837083A
Application number: CNA2006100673863A
Authority: CN
Inventors: 梅泽浩之; 井关正博; 对比地元幸
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2005-03-22
Filing date: 2006-03-22
Publication date: 2006-09-27
Also published as: US20060231472A1; JP4326489B2; JP2006263500A; TWI318966B; TW200635864A; US7396458B2; KR20060102508A; KR100981011B1

Abstract

A wastewater treatment equipment of an embodiment of the present invention neutralizes a WTBT 12 by introducing the WTBT 12 containing fluorine components to a first treatment tank 11 A and by introducing an NaOH solution from a second path P 2 and so on. The fluorine components contained in the WTBT 12 is then fixed as calcium fluoride by adding calcium components to the WTBT 12 stored in a second treatment tank 11 B. Furthermore, MTBR like calcium fluoride are separated from the WTBT in a third treatment tank 11 C. The separated MTBR are rinsed and dewatered in a filter press 17.

Description

Discharged water treatment device

Technical Field

The present invention relates to a discharged water treatment apparatus for separating a removed substance containing a hydrofluoric acid component from treated water.

Background

Currently, from the ecological point of view, it is a very important subject to reduce industrial waste or to separate and reuse industrial waste. Among the industrial wastes, there are various fluids containing the removed substances.

Although they can be expressed by various terms such as sewage, drainage, waste liquid, etc., a liquid containing a substance to be removed in a fluid such as water or a chemical is hereinafter referred to as drainage. These drainage waters are sometimes subjected to removal of the removed matter by an expensive filtration treatment apparatus or the like, so that the drainage waters become a clean fluid and are reused. In addition, the removed material separated from the discharged water may be disposed of as industrial waste. In particular, water is filtered to be in a clean state satisfying environmental standards, and is discharged into the natural world such as rivers and oceans, or is reused.

A large amount of discharged water is generated in the middle of the process of manufacturing a semiconductor device. In the etching step, the exhaust water containing fluorine such as hydrofluoric acid is discharged. It is known that when discharged water having a high concentration of fluorine components flows out to the nature, the balance of the ecosystem is disturbed. Therefore, it is industrially extremely important to remove the fluorine component from the effluent water.

On the other hand, the discharge conditions of the discharged water containing fluorine components are determined by the water pollution prevention law, the regulations of local autonomous bodies, and the like. Specifically, the concentration of the fluorine component contained in the effluent water must be 8mg/L or less. In addition, the total amount of the fluorine component to be discharged may be limited.

As a method for removing the fluorine component, many methods have been proposed. As a method for removing fluorine components contained in the effluent water, a method of performing biological treatment and chemical treatment in different treatment tanks has been proposed (see patent document 1 below). As another method for removing the fluorine component, there is a method (see patent document 2 below) in which a plurality of reaction tanks are prepared, a calcium component is added to raw water stored in one reaction tank to form a seed agent containing a gel-like substance, and the seed agent is added to raw water stored in the other storage tank to treat the fluorine component. Further, there is a method of treating sludge by coagulating and precipitating fluorine components contained in the discharged water with a polymer coagulant.

[ patent document 1]Japanese patent application laid-open No. 2001-54792

[ patent document 2]Japanese patent application laid-open No. Hei 6-312190

However, the method for treating wastewater containing fluorine components described in patent document 1 requires a wastewater treatment step repeated several times, and thus has a problem that the facility becomes large. Therefore, the cost required in the wastewater treatment increases. In addition, since the treatment using biological organic components is performed, there is a problem that it is difficult to perform stable wastewater treatment.

In the method for treating wastewater described in patent document 2, since the concentration of the fluorine component contained in the wastewater is extremely low, there is a problem that another treatment step such as coagulation and precipitation treatment is required to solidify the obtained fluorine component.

Further, when the fluorine component in the effluent water is removed by a coagulation-precipitation method using a commercially available polymer flocculant, there is a problem that a large amount of sludge is generated as an industrial waste. In addition, there is a problem that it is difficult to reuse sludge in which a large amount of flocculant is mixed.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a wastewater treatment apparatus for removing fluorine components from water to be treated without using a flocculant.

The present invention provides a wastewater treatment apparatus, comprising: a neutralizing means for neutralizing the water to be treated into which the fluorine-containing material to be removed has been mixed, a generating means for generating calcium fluoride by adding a calcium component to the water to be treated, and a separating means for separating the material to be removed containing the calcium fluoride from the water to be treated.

Further, the wastewater treatment apparatus of the present invention includes: a 1 st tank for storing water to be treated into which a fluorine-containing material to be removed is mixed, a neutralization means for adding an alkali source to the 1 st tank to neutralize the water to be treated, a 2 nd tank for storing the water to be treated after the neutralization treatment, a generation means for generating calcium fluoride by adding a calcium component to the 2 nd tank, a 3 rd tank for storing the water to be treated containing the calcium fluoride, and a separation means for separating the material to be removed containing the calcium fluoride stored in the 3 rd tank from the water to be treated.

In addition, the discharged water treatment apparatus of the present invention is characterized in that theneutralizing mechanism maintains the pH of the treated water to be between 7 and 8.

In the wastewater treatment apparatus according to the present invention, the separation means is a filter device immersed in the water to be treated.

In addition, the wastewater treatment apparatus according to the present invention is characterized in that the water to be treated is filtered by a self-forming membrane formed on the surface of the filter device.

The wastewater treatment apparatus according to the present invention is characterized by comprising a dewatering mechanism for dewatering the removed material separated from the wastewater.

The wastewater treatment apparatus according to the present invention is characterized by comprising a removing means for removing neutralized salts from the removed matter separated from the wastewater.

In the wastewater treatment apparatus according to the present invention, the generation means adds calcium chloride to the water to be treated.

In addition, the drain water treatment apparatus of the present invention is characterized in that the removed material obtained by periodically peeling the self-formed film is added to the 2 nd tank.

According to the wastewater treatment apparatus of the present invention, calcium fluoride is generated after the water to be treated containing the fluorine component is neutralized by the neutralizing means. Therefore, a sufficient amount of calcium component necessary for immobilizing the fluorine component contained in the water to be treated can be added to the water to be treated, and a removed material having a high calcium fluoride content can be obtained. Therefore, the obtained calcium fluoride can be easily reused. Further, fluorine components can be removed from the water to be treated to a high degree.

Drawings

Fig. 1 is a schematic diagram illustrating a discharged water treatment apparatus according to the present invention.

Fig. 2 is a flowchart illustrating a treatment method using the wastewater treatment apparatus of the present invention.

Fig. 3 is a characteristic diagram illustrating characteristics of the discharged water treatment apparatus of the present invention.

Fig. 4 is a schematic diagram illustrating a discharged water treatment apparatus according to the present invention.

Fig. 5 is a diagram illustrating a filtering device applied to the discharged water treatment apparatus of the present invention.

Fig. 6(a) is a diagram illustrating the operation principle of the filter device of the present invention, and (B) is an enlarged view of the 1 st filter.

Fig. 7 is a diagram illustrating a filter device embodying the present invention.

Fig. 8 is a perspective view (a), a perspective view (B), and a perspective view (C) illustrating the filter device of the present invention.

Fig. 9 is a sectional view (a) and a sectional view (B) illustrating the regeneration of the filter device of the present invention.

Among them, 10 treatment apparatus,

11A treatment tank

1, 11B treatment tank 2, 11C treatment tank 3, 11D treatment tank 4, 12 treated water, 13 filtration membrane, 15A

chemical tank

1, 15B chemical tank 2, 15C storage tank, 16 filtered water, 17 filter press, 18 gas diffusion apparatus, 19 receiving tank, 20A power supply, 20B cathode, 20C anode

Detailed Description

In the present embodiment, the configuration of the wastewater treatment apparatus 10 for treating water to be treated (wastewater) containing a fluorine component and a method for treating wastewater using the same will be described. Fig. 1 is a diagram showing a configuration of a discharged water treatment apparatus 10, fig. 2 is a flowchart showing a method of treating discharged water, and fig. 3 is a graph showing an experimental result.

The structure of the wastewater treatment apparatus 10 will be described with reference to fig. 1. The wastewater treatment apparatus 10 of the present embodiment mainly includes: a first treatment tank 11A for storing and neutralizing water to be treated 12 containing hydrofluoric acid, a second treatment tank 11B for adding a calcium component to a fluorine component contained in the water to be treated 12 subjected to neutralization treatment to produce calcium fluoride, a third treatment tank 11C for separating calcium fluoride from the water to be treated 12, and a filter press 17 for obtaining solid calcium fluoride. With the wastewater treatment apparatus 10 having such a configuration, fluorine components can be removed from the water to be treated, and high-purity calcium fluoride can be obtained.

First, the water to be treated 12 will be described. The water to be treated in the present embodiment is effluent containing fluorine components. The effluent is discharged in a process of etching in a semiconductor manufacturing plant. More specifically, a large amount of discharged water containing fluorine is discharged from a step of etching a semiconductor, glass, metal, or the like. In these etching steps, hydrofluoric acid is used to improve the corrosiveness during etching. Here, hydrofluoric acid is an aqueoussolution of Hydrogen Fluoride (HF). Therefore, hydrofluoric acid is contained in the effluent discharged from this step, which is very dangerous.

The following describes each element constituting the wastewater treatment apparatus 10 of the present embodiment in detail.

The 1 st path P1 is a water path such as a pipe, and the water to be treated 12 containing hydrofluoric acid is treated by this pathIs conveyed to the 1 st treatment tank 11A. A pump for transporting the water to be treated may be provided on the way of the 1 st path P1. Since the hydrofluoric acid wastewater is a strong acid having a pH of about 2, the 1 st treatment tank 11A is made of a material such as glass having excellent acid resistance. The water 12 supplied from the 1 st path P1 contains about 10,000mg/L of fluorine component (F)^-)。

The capacity of the 1 st treatment tank 11A is preferably about 3 times as large as the following 2 nd treatment tank 11B and 3 rd treatment tank 11C. Thus, the water 12 to be treated intermittently discharged is stored in the 1 st treatment tank 11A, and the stored water 12 to be treated is continuously treated in the 2 nd treatment tank 11B and the 3 rd treatment tank 11C.

The 2 nd route P2 and the 3 rd route P3 function as a neutralizing mechanism for supplying the neutralizing agent (NaOH) stored in the 1 st chemical tank 15A to the 1 st processing tank 11A. Here, for example, an aqueous solution containing 25% by weight of NaOH is used as the neutralizing agent. By supplying the neutralizing agent through these paths, the pH of the water 12 stored in the 1 st treatment tank 11A is adjusted to, for example, 7 to 8. By performing the neutralization treatment of the water 12 to be treated in this manner, neutralized salts are formed, but the neutralized salts are removed later. The method for removing the neutralized salt will be describedlater.

The 2 nd path P2 is provided with a large 1 st pump Po1, and the 2 nd path P3 is provided with a relatively small 2 nd pump Po 2. By supplying the neutralizing agent through a plurality of paths provided with pumps having different outputs, the water 12 to be treated can be neutralized early and accurately. Specifically, when the neutralizing agent is continuously supplied to the water 2 to be treated, the value thereof changes rapidly in the vicinity of pH 7. Therefore, when the pH is low (for example, pH less than 6), the pH can be changed early by supplying the neutralizing agent through the 2 nd path P2 where the 1 st pump Po1 having a large output is provided. Further, if the pH becomes high (for example, pH 6 or more), the pH of the water 12 can be accurately controlled to be near neutral (pH 7) by supplying the neutralizing agent only through the 3 rd path P3 provided with the 2 nd pump Po2 having a small output. In the first treatment tank 11A, 99.9% or more of Hydrogen Fluoride (HF) is dissociated into hydrogen ions (H)⁺) And fluorine ion (F)^-) (the following formula A). In the first treatment tank 11A, the water 12 to be treated may be stirred by a stirring mechanism such as a stirring paddle in order to promote the dissociation.

Formula A

The 4 th path P4 is a path for transporting the water 12 neutralized in the 1 st treatment tank 11A to the 2 nd treatment tank 11B where fluorine components are fixed. The pump provided in the 4 th path P4 may be turned ON or OFF according to the amount of the water 12 stored in the 1 st treatment tank 11A. For example, the pump provided in the 4 th path P4 may be operated only when the amount of water 12 stored in the 1 st treatment tank 11A is equal to or more than half of its capacity. With this arrangement, the water 12 to be treated can be always stored in the first treatment tank 11A at a capacity of at least half of the capacity. Therefore, even when a large amount of the water 12 to be treated of a strong acid flows into the 1 st treatment tank 11A from the 1 st pathway P1, the pH of the water 12 to be treated stored in the 1 st treatment tank 11A can be prevented from rapidly changing.

The 5 th path is a path for supplying the calcium component from the 2 nd chemical tank 15B to the 2 nd retention tank. Specifically, calcium chloride (CaCl) stored in the 2 nd medicine tank 15B₂) The aqueous solution (e.g., 30 wt%) is supplied to the 2 nd treatment tank 11B through the 5 th path P5. By adding calcium chloride, the fluorine component contained in the water 12 to be treated is treated as CaF₂(calcium fluoride) (the following formula B). Since the solubility product of calcium chloride is very high, a large amount of calcium chloride can be supplied to the water 12 to be treated. For example, by reacting calcium ion (Ca)²⁺) By adding calcium chloride to the water 12 to be treated so as to be 200mg/L or more, the fluorine ions (F) contained in the water 12 can be removed^-) The concentration of (b) is set to 8mg/L or less. The concentration of the fluoride ion satisfies a general emission standard.

Formula B

The calcium chloride stored in the treatment tank 2B may be introduced into the treatment tank 2C for solid-liquid separation. In this way, since the fluorine component can be immobilized also in the 3 rd treatment tank 11C, the fluorine component contained in the filtered water can be further reduced.

Instead of the calcium chloride, slaked lime (Ca (OH)) may be added to the treatment tank 2 11B₂). The added slaked lime acts as a seed agent for fixing the fluorine component, and therefore,the fixation of the fluorine component can be promoted.

In addition, in the treatment tank 11B of the 2 nd treatment tank 11, the particles of calcium fluoride can be increased to, for example, 0.25 μm or more by aging the water 12 to be treated. This operation has an advantage that membrane separation of calcium fluoride can be easily performed. In addition, in the treatment tank 2 11B, the pH is maintained between 7 and 8. By these operations, there is an advantage that a colloidal substance is not generated, and a filtration membrane is not clogged in a subsequent step, so that filtration becomes easier.

The 6 th path P6 is a path for transferring the water 12 containing calcium fluoride from the 2 nd treatment tank 11B to the 3 rd treatment tank 11C.

In the 3 rd treatment tank 11C, the removed matter containing calcium fluoride is separated from the water 12 to be treated. Here, the removed matter is separated from the water 12 by the filtering action of the filtering membrane 13 immersed in the water 12 stored in the 3 rd treatment tank 11C.

The filter membrane 13 is immersed in the water 12 to be treated stored in the treatment tank 11, and has a function of filtering the water 12 to be treated. As the filter membrane 13 used, all of filter means capable of filtering in a fluid may be used. In this embodiment, the solid-liquid separation of calcium fluoride and the water 12 to be treated is performed by performing filtration using a self-forming membrane formed on the surface of the filtration membrane 13. Details of the self-forming film will be described later.

The self-forming film may be a self-forming film made of a calcium fluoride-containing material to be removed which is generated in the water 12 to be treated. That is, the water 12 to be treated is filtered by the removed matter adsorbed on the filtration surface of the filtration membrane 13. In addition, when the calcium fluoride is recovered, the self-formed film is also peeled off from the filtration membrane 13 and recovered.

The gas diffuser 18 has a function of supplying bubbles to the filtration membrane 13 from below in the water 12 to be treated. Specifically, the gas is supplied to the gas diffuser 18 from a pump or the like, not shown, provided outside. Thus, the bubbles 19 generated from the gas diffuser 18 move upward along the filtering surface of the filtering membrane 13. By generating bubbles from the gas diffuser 18 in this manner, the thickness of the self-formed film formed on the surface of the filtration membrane 13 can be set to a constant value or less. As a result, the filtration of the water 12 to be treated can be performed while suppressing clogging of the self-forming membrane and securing a certain degree of flux.

As the gas generated from the gas diffuser 18, an inert gas such as helium, neon, argon, or nitrogen can be used. When air is supplied from the gas diffuser 18 to the water 12, carbon dioxide contained in the air reacts with fluorine contained in the water 12, and the concentration of calcium fluoride may be reduced. This possibility can be eliminated by using an inert gas as the gas supplied by the gas diffuser 18.

The 7 th path P7 is a path through which filtered water filtered by the filter membrane 13 passes. The filtered water 16 is stored in the storage tank 15C provided on the way of the 7 th path P7. Most of the filtered water passing through the 7 th path P7 is reused or discharged to nature such as a river.

The filtered water passing through the 7 th path P7 may also be subjected to a purification process for reuse or discharge. As the purification treatment, pH adjustment, removal of nitrogen components, removal of calcium components, and the like are performed. In orderto adjust the pH, after the pH of the water to be treated is measured, an alkaline substance or an acidic substance is added to the water to be treated. In this embodiment, a denitrification method using an electrode is employed for the removal of nitrogen components. The details of the denitrification method will be described later. In addition, the calcium component contained in the water 12 is treated by the electric field and becomes CaCO₃To the water 12 to be treatedThe surface of (2) is floated and recovered. The treated water thus treated is reused or discharged.

The storage tank 15C stores a part of the filtered water filtered by the filtering membrane 13, and the position thereof is set above the liquid surface of the water 12 to be treated stored in the 3 rd treatment tank 11C. The filtered water stored in the storage tank 15C flows back to the 7 th path P7 to be used when the self-forming membrane formed on the surface of the filtration membrane 13 is peeled off. Details of this matter will be described later.

The 8 th path P8 is a path for conveying the solidified removed material from the 3 rd treatment tank 11C to the filter press machine 17. Specifically, the removed matter deposited on the surface of the filtration membrane 13 and the removed matter deposited in the lower portion of the 3 rd treatment tank 11C are sent to the filter press 17. The transported treated water 12 contains calcium fluoride with high purity.

The removed material containing calcium fluoride is supplied to the filter press machine 17 through the 8 th path P8, and the water content of the removed material is reduced by performing dehydration treatment. The water content of the removed material dehydrated by the filter press machine 17 is, for example, about 50% by weight. Further, when the removed matter was dried, a bulk material having a purity of calcium fluoride of about 85% by weight was obtained. Calcium fluoride contained in the removed product in high purity is reused as a fluorine source.

The 9 th path P9 is a path for washing the neutralized salt contained in the removed material stored in the filter press machine 17 by injecting water into the filter press machine 17. By injecting water into the filter press machine 17, the purity of calcium fluoride contained in the removed material stored in the filter press machine 17 can be improved. The removed material neutralized in the 1 st treatment tank 11A contains about 15% by weight of a neutralizing salt (NaCl). By injecting water into the filter press machine 17 through the 9 th path P9, most of the neutralized salt is discharged from the filter press machine 17 to the outside. In addition, calcium fluoride, which is larger in size than the neutralized salt, remains inside the filter press 17.

The water injected into the filter press machine 17 is temporarily stored in the receiving tank 19. The treated water stored in the receiving tank 19 is returned to the 3 rd treatment tank 11C through the 10 th path P10, and is subjected to filtration treatment.

The 11 th path P11 is a path for conveying the removed material dehydrated by the filter press machine 17 to the 2 nd treatment tank 11B for producing calcium fluoride. In the filter press machine 17, the removed material deposited on the surface of the filter membrane 18 is stored, and the removed material contains calcium fluoride at a high concentration. Therefore, by returning the removed material mainly composed of calcium fluoride to the 2 nd reaction tank, the chemical reaction in the 2 nd treatment tank 11B can be promoted, and most of the fluorine component contained in the water 12 to be treated can be immobilized as calcium fluoride.

The above is the configuration of the discharged water treatment apparatus 10 according to thepresent embodiment. Here, the 2 nd processing bath 11B and the 3 rd processing bath 11C may be the same processing bath. With this arrangement, the fluorine component can be fixed and the solid-liquid separation can be performed in the same tank, and the entire facility can be downsized.

Next, a method of treating discharged water using the discharged water treatment apparatus 10 will be described with reference to fig. 2. The method for treating wastewater according to the present embodiment comprises: a 1 st step S1 of storing hydrofluoric acid discharged water, a 2 nd step S2 of neutralizing the water to be treated, a 3 rd step S3 of generating calcium fluoride, a 4 th step S4 of performing solid-liquid separation of calcium fluoride, a 5 th step S5 of removing neutralization salts from the removed matter, and a 6 th step S6 of recovering calcium fluoride. Referring also to fig. 1, the steps will be described in detail.

In step S1, the water 12 to be treated discharged from the etching equipment of the semiconductor factory or the like is stored in the 1 st treatment tank 11A. Here, the water to be treated 12 which is hydrofluoric acid is a strong acid having a pH of about 2.

In step S2, the water to be treated 12 stored in the 1 st treatment tank 11A is neutralized. This neutralization treatment is performed by adding NaOH stored in the 1 st chemical tank 15A to the 1 st treatment tank 11A. The pH of the water 12 stored in the 1 st treatment tank 11A is monitored, and NaOH is added to the water 12 so that the pH of the water 12 becomes about 7 to 8. Here, KOH may be used as the neutralizing agent in addition to NaOH. The neutralized water 12 is sent to the 3 rd treatment tank through the 4 th path P4.

In step S3, calcium fluoride is generated by adding a calcium component to the water 12 containing a fluorine component to fix the fluorine component. Here, calcium chloride (CaCl) was used as the fluorine component to be added₂) E.g., 30 wt-%. Even when the water 12 to be treated contains a large amount of fluorine components, since calcium chloride has high solubility, a large amount of calcium chloride can be added to the water 12 to be treated, and most of the fluorine components contained can be immobilized. The water to be treated 12 in which the fluorine component contained is immobilized as calcium fluoride is sent to the 3 rd treatment tank 11C.

In step S4, the removed material containing calcium fluoride is separated from the water 12 by membrane filtration. As a mechanism for performing filtration, in the present embodiment, a self-forming membrane composed of removed substances deposited on the surface of the filtration membrane 13 is used. The filtered water filtered by the filter membrane 13 is discharged to the outside, subjected to further treatment such as pH adjustment, and reused or discharged to the natural world. In the filtration method using a self-forming membrane, since the flux of the self-forming membrane gradually decreases, the self-forming membrane is periodically peeled off and formed again. When the self-formed membrane is peeled off, the filtered water is caused to flow back from the storage tank 15C to the filtration membrane. Thus, the filtration membrane deposited on the surface of the filtration membrane 13 is peeled off and deposited in the lower part of the 3 rd treatment tank 11C. In addition, during the filtration of the water 12 to be treated by the filtration membrane 13, bubbles are caused to pass through the surface of the filtration membrane 13 by the gas diffusion device 18. Thus, the filtration ability can be maintained by controlling the thickness of the self-formed membrane formed on the surface of the filtration membrane 13. The removed matter concentrated in this step is sent to the filter press 17.

In step S5, water is injected into the filter press machine 17 to wash and remove the neutralized salt (NaCl) contained in the removed material. Since the water to be treated 12 subjected to neutralization contains a neutralization salt, the material to be removed separated from the water to be treated 12 contains a neutralization salt in addition to calcium fluoride. By injecting water into the filter press 17, the neutralized salt is dissolved in the water and discharged to the outside. Since calcium fluoride has a large diameter, it cannot be discharged to the outside from the filter press 17 even when washed with water. By this step, the concentration of calcium fluoride contained in the removed matter is increased.

In step S6, calcium fluoride is recovered. Specifically, after the removed object is dehydrated by the filter press machine 17, the removed object in a semi-solid state is taken out. In this state, the water content of the removed material was about 50 wt%. Then, the removed material is dried to form a solidified removed material block. In this embodiment, a removed material containing 85% by weight of calcium fluoride can be obtained.

In the present embodiment, since the solid-liquid separation treatment is performed without using a flocculant such as a polymer flocculant, it is possible to obtain immobilized calcium fluoride from the fluorine-containing effluent water with high purity. The obtained calcium fluoride can be reused as hydrofluoric acid in a semiconductor production process or the like by reacting it with a strong acid (e.g., sulfuric acid). The high-purity calcium fluoride obtained in the present application may be used as a flux to be mixed into steel. Further, if hydrochloric acid is added to the obtained calcium fluoride, calcium chloride can also be obtained. Further, since sulfuric acid, hydrochloric acid, or the like added for recycling calcium fluoride is a chemical product that is prepared in a semiconductor factory, calcium fluoride can be recycled without adding new equipment to the factory.

In the present embodiment, after the water to be treated is neutralized with NaOH or the like, calcium chloride (CaCl) is used₂) The fluorine is fixed. Therefore, since most of the calcium component added reacts with the fluorine component contained in the water to be treated, the ratio of calcium fluoride to the removed material can be increased.

In addition, the neutralized salt generated by the neutralization treatment is removed by the washing treatment. This also helps to increase the purity of the calcium fluoride relative to the removed material.

Next, an experiment for filtering the water to be treated 12 using the filter membrane 13 shown in fig. 1 will be described with reference to fig. 3. Fig. 3 is a graph showing the change with time of the flux when the filtering treatment is performed. In the graph, the horizontal axis represents the time during which the treatment is continuously performed, and the vertical axis represents the magnitude of the flux.

First, the conditions of the experiment will be described. In this experiment, the thickness of the sample is 0.1m²The filtration was performed by applying a suction pressure of 7kPa to the filtration membrane having the area of (1). Calcium chloride was added to the effluent containing 1000mg/L of fluoride ions in the water to be treated, and the fluoride component was immobilized as calcium fluoride. The calcium fluoride has a diameter of about 0.25. mu.m. Further, experiments were conducted by periodically metering the amount and flux of treated water being treated.

According to this experiment, the average flux was 0.4m/day, and the filtration membrane 13 of this mode proved to be sufficiently durable for practical use. The concentration of the fluorine component contained in the filtered water obtained by the filtration membrane was 3.5mg/L, which satisfied the standard of general discharge.

Specifically, when a substance to be removed such as calcium fluoride is circulated to form a self-formed film on the surface of the filtration membrane, filtration is started at a point when filtered water having a transparency of at least a certain level is obtained.

The flux at the time when filtration started was about 0.7m/day, and when filtration was continued, the flux slowly decreased. This is because the degree of clogging of the self-forming membrane increases as the filtration proceeds. The flux at the time when 130 minutes passed after the start of filtration was about 0.2 m/day. At this time, the self-formed membrane is peeled off from the filtration membrane, and the removed matter concentrated in the water to be treated is collected.

After the self-formed membrane is peeled off and the removed matter is recovered, a new self-formed membrane is formed on the surface of the filtration membrane, and the water to be treated is filtered again. By repeating the above steps, the removed material containing calcium fluoride can be separated from the water to be treated.

From the experiments, it is apparent that sufficient flux can be ensured by periodically performing peeling and regeneration from the formed film.

In the present embodiment, a method of removing nitrogen components and the like from the treated water obtained by the above-described wastewater treatment apparatus 10 will be described. FIG. 4 is a view showing the structure of the 4 th treatment bath 11D for removing nitrogen components.

Into the 4 th treatment tank 11D, the water to be treated 12 from which the fluorine component has been removed by the treatment apparatus 10 is introduced. Thereafter, a voltage is applied to the electrode pair at least partially immersed in the water 12 to remove nitrogen components contained in the water 12. The following will explain the details of the removal of such nitrogen components.

The pair of electrodes immersed in the water to be treated is composed of an anode 20A and a cathode 20B, and has a power supply 20C for applying a voltage to both electrodes. Further, a control mechanism for controlling the power source 20C and a stirring mechanism for stirring the water to be treated 12 in the tank may be provided.

The cathode 20B may be formed of a material containing a conductor of group 1B, group 2B or group 8 of the periodic table or a material in which the conductor is covered with the same group. Specifically, the cathode 20B is composed of an alloy or sintered body of copper, iron, copper and zinc or copper and iron or copper and nickel or copper and aluminum.

The anode 20A may be an insoluble electrode made of an insoluble metal such as platinum, iridium, palladium, or an oxide thereof, or carbon. Further, by providing a shielding wall surrounding the anode 20A, it is possible to prevent oxygen bubbles generated from the anode 20A from moving toward the cathode 20B.

A method of treating the nitrogen component by the electrode 12 configured as described above will be described.

The water to be treated 12 is immersed in the pair of the anode 20A and the cathode 20B to be electrified. In this way, nitrate ions contained in the water to be treated are converted into nitrite ions (formula C) by the reduction reaction on the cathode 20B side. Further, nitrite ions generated by the reduction reaction of nitrate ions are converted into ammonia (formula D) by the reduction reaction. The following formulae C and D are shown.

Formula C

Formula D

On the other hand, on the anode 20A side, active oxygen or hypochlorous acid is generated from the surface of the anode 20A, and nitrogen gas (formula E) is generated by the denitrification of ammonia in the water to be treated. In order to promote the denitrification reaction of ammonia at the anode 5, a halogen ion such as a chloride ion, an iodide ion, or a bromide ion, or a compound containing such a halogen ion, such as sodium chloride or potassium chloride, is added to the water to be treated. In this case, the chlorine ion of sodium chloride added to the water to be treated is, for example, 10ppm to 40000 ppm. Thus, for example, when sodium chloride is added to water to be treated, the sodium chloride is oxidized at the anode to generate chlorine (formula F), and the generated chlorine reacts with water in the water to be treated to generate hypochlorous acid (formula G). Then, the generated hypochlorous acid reacts with ammonia present in the water to be treated, undergoes a plurality of chemical changes, and is converted into nitrogen gas (formula H). The following formulae E to H are shown. In addition, in this embodiment, since calcium chloride may be added to the water 12 to be treated, chloride ions ionized from the calcium chloride exist in the water 12 to be treated. This result has an advantage that electric field treatment for removing nitrogen components from the water 12 to be treated can be easily performed.

Formula E

Formula F

Formula G

Formula H

Thus, nitrogen compounds such as nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen in the water to be treated can be treated in the tank.

In addition, the calcium component contained in the water to be treated is also changed into CaCO by the electric field treatment₃And floats on the surface of the water 12. Thereafter, by passing the floated CaCO₃The calcium component remaining in the water 12 can be recovered. In addition, the recovered CaCO can be used₃And then is reused. In addition, neutralization treatment for making the pH of the water 12 to be treated near neutral may be performed in the 3 rd treatment tank.

In this embodiment, a detailed description will be given of a filtering mechanism that can be used as the filtering membrane 13 immersed in the water 12 to be treated in embodiment 1. In the following embodiment, a filtration mechanism using a self-forming membrane will be described, but a filtration apparatus of another embodiment may be applied to the present invention.

Referring to fig. 5 and the following drawings, the filter device used in the present embodiment is a device for removing a fluid (water to be treated) mixed with a removed object that is calcium fluoride, by a filter composed of a self-forming film formed of the removed object.

Specifically, the filtration device of this embodiment is a device in which a self-forming film serving as the 2 nd filter 22 made of calcium fluoride as a removed substance is formed on the surface of the 1 st filter 21 made of an organic polymer. The water to be treated mixed with the removed matter is filtered by using the 2 nd filter 22 as the self-forming membrane.

The 1 st filter 21 may be any of organic polymer based filters and ceramic based filters in principle, as long as it can adhere a self-forming film. Here, a polyolefin-based polymer film having an average pore diameter of 0.25 μm and a thickness of 0.1mm was used. A photograph of the surface of the filtration membrane composed of the polyolefin group is shown in fig. 6 (B).

The 1 st filter 21 has a flat membrane structure provided on both surfaces of the frame 24, and is vertically immersed in a fluid. The filtrate 27 is taken out by sucking the filtrate from the hollow portion 25 of the frame 24 by the pump 26.

The 2 nd filter 22 is a self-forming film which adheres to the entire surface of the 1 st filter 21 and is solidified by sucking aggregated particles of the removed object. The self-forming film may be either a gel-like film or a cake-like film.

The 2 nd filter 22 for forming a self-forming film as the above-mentioned removed object and filtration for removing the removed object will be described. The fluid (water to be treated) mixed with calcium fluoride diffuses in the water 12 to be treated in a particulate state.

Referring to fig. 6(a), the 1 st filter 21 has a plurality of filter pores 21A, and the self-forming film of the removed substance formed in a layer shape at the openings of the filter pores 21A and the surface of the 1 st filter 21 is the 2 nd filter 22. The aggregated particles of the removed object composed of calcium fluoride are present on the surface of the 1 st filter 21, and the aggregated particles are sucked by the suction pressure from the pump through the 1 st filter 21, and the moisture of the fluid is sucked off, so that the fluid is dried (dehydrated) and immediately solidified, and the 2 nd filter 22 is formed on the surface of the 1 st filter 21.

Since the 2 nd filter 22 is formed of aggregated particles of the object to be removed, the film thickness is directly set to a predetermined film thickness, and filtration of the aggregated particles of the object to be removed is started by the 2 nd filter 22. Therefore, when the filtration is continued while the suction is performed by the pump 26, the self-forming film of the aggregated particles is stacked on the surface of the 2 nd filter 22 to increase the thickness, and the 2 nd filter 22 is quickly clogged and the filtration cannot be continued. While the calcium fluoride of the removed matter is solidified and adheres to the surface of the 2 nd filter 22, and the water to be treated passes through the 1 st filter 21 and is taken out as filtered water.

In fig. 6(a), the water to be treated mixed with the removed matter is present on one side of the 1 st filter 21, and the filtered water passing through the 1 st filter 21 is produced on the opposite side of the 1 st filter 21. The water to be treated is sucked and flows in the direction of the arrow, and the aggregated particles in the water to be treated 12 are solidified by the suction while approaching the 1 st filter 21. Further, the self-forming membrane to which a plurality of aggregated particles are bonded is adsorbed on the surface of the 1 st filter 21 to form the 2 nd filter 22. The 2 nd filter 22 functions to filter the water to be treated while solidifying the removed substances in the solution.

By gradually sucking the water to be treated of the solution through the 2 nd filter 22 in this way, the water in the water to be treated is taken out as filtered water, and the removed object is dried and solidified, and is stacked on the surface of the 2 nd filter 22, whereby the aggregated particles of the removed object are captured as a self-forming film.

The 1 st filter 21 is vertically immersed in the water to be treated, and the water to be treated is in a state in which the removed matter is dispersed. When the water to be treated is pumped by the pump 26 through the 1 st filter 21 at a weak pumping pressure, the aggregated particles of the matter to be removed on the surface of the 1 st filter 21 are bonded to each other and adsorbed on the surface of the 1 st filter 21. Further, although the aggregated particles S1 having a diameter smaller than that of the filter pores 21A pass through the 1 st filter 21, there is no problem because the filtered water is circulated again into the water to be treated in the step of forming the 2 nd filter 22 into a membrane. In this film formation step, since the suction is performed with an extremely weak suction pressure, the aggregated particles S1 are stacked while forming various gaps, and become the No. 2 filter 22 of a flexible self-formed film having an extremely high degree of swelling. The water in the water to be treated permeates the self-forming membrane having a high degree of swelling and is sucked, passes through the 1 st filter 21, and is taken out as filtered water, and the water to be treated is finally filtered.

Further, by sending the air bubbles a from the bottom surface of the water to be treated, a fluid is formed along the surface of the 1 st filter 21 in parallel with the water to be treated. This is because the 2 nd filter 22 is uniformly attached to the entire surface of the 1 st filter 21, and is flexibly attached with a gap formed in the 2 nd filter 22. Specifically, although the air flux is set to 1.8 liters/minute, it may be selected according to the membrane quality of the 2 nd filter 22.

Then, in the filtration step, the aggregated particles S1 composed of calcium fluoride were gradually stacked on the surface of the 2 nd filter 22 while being adsorbed by a weak suction pressure. At this time, the purified water permeates the 2 nd filter 22 and the stacked aggregated particles S1, and is taken out as filtered water from the 1 st filter 21.

However, when the filtration is continued for a long time, the self-forming film is attached to the surface of the 2 nd filter 22 in a thick state, and therefore the above gap is quickly clogged, and the filtered water cannot be taken out. For this reason, in order to regenerate the filtration ability, it is necessary to remove the laminated self-forming membrane.

Next, a more specific filtering apparatus will be described with reference to fig. 7.

In fig. 7, a pipe 24 is provided as a means for supplying water to be treated above the treatment tank 11. The pipe 24 guides the fluid mixed with the removed material into the processing tank 11. Here, the effluent containing calcium fluoride by adding a calcium component to the effluent containing hydrofluoric acid is introduced into the treatment tank 11.

A plurality of filter devices 23 each forming a 2 nd filter are provided in the water 12 to be treated stored in the treatment tank 11. Below the filter device 23, a gas diffusion device 18 such as a bubbling device used in a fish tank or a pipe is provided. The position is adjusted to just pass through the surface of the filter device 23. The gas diffusion means 18 is disposed across the entire bottom edge of the filter means 23, so that the bubbles can be uniformly supplied to the entire surface of the filter means 23. And 25 is an air pump.

The filtered fluid filtered by the filter device 23 flows through the pipe 25 fixed to the filter device 23, and is connected to the magnetic pump 35 for suction through the valve V1. Line 29 is connected from magnetic pump 35 through control valve CV1 to valve V3 and valve V4. Further, a 1 st pressure gauge 30 is provided after the valve V1 of the pipe 25, and the suction pressure Pin is measured. Further, a flow meter 28 and a 2 nd pressure gauge 27 are provided after the control valve CV1 of the pipe 29, and the flow meter 28 controls the flow rate to a constant value. In addition, the gas flux from the gas pump 25 is controlled by a control valve CV 2.

The water 12 to be treated supplied through the pipe 24 is stored in the treatment tank 11 and filtered by the filter device 23. The bubbles pass through the surface of the 2 nd filter 22 attached to the filter device, and the parallel flow is generated by the lifting force or the collapse of the bubbles, and the removed objects adsorbed on the 2 nd filter 22 are moved and uniformly adsorbed on the entire surface of the filter device 23, thereby maintaining the filtering ability without lowering.

Here, the above-described filter device 23, specifically, the filter device 23 immersed in the treatment tank 11 will be described with reference to fig. 8.

Reference numeral 30 shown in fig. 8(a) is a frame having a frame-like shape, and has a function of supporting the entire filter device 23.

Filtration membranes

31 and 32 to be the 1 st filter 21 are bonded and fixed to both surfaces of the frame 30. Further, the filtrate filtered by the

filter membranes

31 and 32 flows into the inner space 33 surrounded by the frame 30 and the

filter membranes

31 and 32 through the suction duct 34. Further, the filtered water is taken out through a pipe 34 sealingly attached to the frame 30. The filter membranes 31, 32 and the frame 30 are completely sealed so that the treated water does not intrude into the space 33 from outside the filter membranes.

Since the

filter membranes

31 and 32 in fig. 8(a) are thin resin films, they may be warped inward or broken when sucked. The film solving this problem is fig. 8 (B). In fig. 8(B), only 9 spaces 33 are shown, but actually, a large number of spaces are formed. The filtration membrane 31 used in practice is a polyolefin-based polymer membrane having a thickness of about 0.1 mm. Further, as shown in fig. 8(B), the thin filter membrane is formed into a bag shape, here denoted by FT. A frame 30 having a duct 34 integrated therewith is inserted into the bag-shaped filter membrane FT, and the frame 30 and the filter membrane FT are bonded to each other. Reference numeral RG denotes a pressing mechanism, which presses the frame to which the filter membrane FT is bonded from both sides. The filter membrane FT is exposed from the opening OP of the pressing mechanism.

Fig. 8(C) shows a device in which the filter device 23 itself is formed into a cylindrical shape. The frame attached to the duct 34 is cylindrical, and has openings OP1 and OP2 on the side surfaces. Since the side surfaces corresponding to the openings OP1 and OP2 are removed, a support mechanism SUS for supporting the filter membrane 31 is provided between the openings. Thus, the filter membrane 31 is attached to the side surface.

Next, an actual filtering method will be described in detail with reference to the mechanism shown in fig. 7. First, the water to be treated 12 mixed with the fluorine-containing material to be removed is introduced into the treatment tank 11 through the pipe 24. Thereafter, the filtration device 23 of only the 1 st filter 21, in which the 2 nd filter 22 is not formed, is immersed in the treatment tank 11, and the water to be treated is circulated while being sucked by the pump 35 at a weak suction pressure through the pipe 24. The circulation path is a filter 23, a pipe 25, a valve V1, a pump 35, a pipe 29, a control valve CV1, a flow meter 28, a light sensor 26, and a valve V3, and the water to be treated is pumped out of the treatment tank 11 and returned to the treatment tank 11.

Bycirculating the water, a membrane of the 2 nd filter 22 is formed on the 1 st filter 21 of the filter device 23, and finally the removed substance of calcium fluoride as the target substance is captured.

That is, when the water to be treated is pumped by the pump 35 through the 1 st filter 21 at a weak pumping pressure, particles of the removed matter are easily solidified and adsorbed on the surface of the 1 st filter 21. The solidified aggregated particles are adsorbed and laminated on the surface of the 1 st filter 21 at a portion larger than the filtration pores 21A of the 1 st filter 21, thereby forming a 2 nd filter 22 composed of a self-forming membrane. Further, the aggregated particles pass through the 1 st filter 21, but at the same time as the film formation by the 2 nd filter 22, the water in the water to be treated is sucked through the formed film as a passage and is taken out as purified water, thereby filtering the water to be treated.

The concentration of the aggregated particles contained in the filtered water was monitored by the optical sensor 26, and when the aggregated particles were confirmed to be less than a desired mixing ratio, filtration was started. When the filtration is started, the valve V3 is closed by the detection signal from the optical sensor 26, the valve V4 is opened, and the circulation path is closed. Therefore, the purified water is taken out from the valve V4. The bubbles of air always supplied from the air pump 25 are supplied from the gas diffusion means 18 to the surface of the filter means 23 while being regulated by the control valve CV 2.

When the filtration is continuously performed in this manner, the water in the water to be treated in the treatment tank 11 is taken out of the treatment tank 11 as purified water, and therefore the concentration of the removed substances in the water to be treated increases. That is, the water 12 to be treated is concentratedto increase the viscosity. Therefore, the water to be treated is replenished from the pipe 24 to the treatment tank 11, and the increase of the concentration of the water to be treated is suppressed to improve the efficiency of filtration. However, the self-forming film is attached to the surface of the 2 nd filter 22 of the filter device 23 in a thick state, and the 2 nd filter 22 is rapidly clogged, so that the filtration is impossible.

When the 2 nd filter 22 of the filter device 23 is clogged, the filtering ability of the 2 nd filter 22 is regenerated. That is, the pump 35 is stopped, and the negative suction pressure applied to the filter device 23 is released.

The regeneration step will be described in further detail with reference to a schematic diagram of fig. 9. Fig. 9(a) shows a state of the filter device 23 in the filtering step. Since the hollow portion of the 1 st filter 21 becomes a negative pressure with respect to the outside due to a weak suction pressure, the 1 st filter 21 becomes a shape recessed inward. Therefore, the 2 nd filter 22 adsorbed on the surface thereof is similarly formed into a shape recessed inward. In addition, the self-formed film gradually adsorbed on the surface of the 2 nd filter 22 is also the same.

However, referring to fig. 9(B), since the weak suction pressure is stopped and the pressure is returned to substantially the atmospheric pressure in the regeneration step, the 1 st filter 21 of the filter device 23 is returned to the original state. In this way, the 2 nd filter 22 and the self-formed film adsorbed on the surface thereof are restored in the same manner. As a result, first, the suction pressure to which the self-forming membrane is adsorbed is eliminated, and therefore, when the self-forming membrane loses the adsorption force to the filter device 23, the self-forming membrane receives a force to expand outward at the same time. Thus,the adsorbed self-formed film starts to detach from the filter device 23 by its own weight. In order to accelerate the detachment, the amount of bubbles from the gas diffusion device 18 may be increased by about 2 times. According to the experiment, the separation starts from the lower end of the filter device 23, and the self-formed film of the 2 nd filter 22 on the surface of the 1 st filter 21 separates like avalanche, and settles to the bottom surface of the treatment tank 11. Thereafter, the 2 nd filter 22 may circulate the water to be treated by the circulation path to form a film again. In this regeneration step, the 2 nd filter 22 is returned to the original state until it is returned to a state in which the filtration of the water to be treated is possible, and the filtration of the water to be treated is performed again.

In addition, when the filtered water is caused to flow backward into the hollow portion 25 in the regeneration step, the first filter 21 is returned to its original state, and the hydrostatic pressure of the filtered water is applied and a force for expanding outward is applied. The filtered water passes through the filter holes 21A from the inside of the 1 st filter 21 and seeps out to the boundary between the 1 st filter 21 and the 2 nd filter 22, and the separation of the self-forming membrane of the 2 nd filter 22 from the surface of the 1 st filter 21 is promoted. The reverse flow can be performed by causing the filtered water 16 temporarily stored in the storage tank 15C shown in fig. 1 to flow into the filtration membrane.

When the filtration is continued while the 2 nd filter 22 is regenerated as described above, the concentration of the removed matter of the water to be treated stored in the treatment tank 11 increases, and the water to be treated soon has a considerable viscosity. Therefore, if the concentration of the removed matter in the water to be treated exceeds a predetermined concentration, the filtration operation is stopped and the water is left standing for precipitation. In this case, the concentrated slurry is left at the bottom of the treatment tank 11, and the cake-like concentrated slurry is recovered. The recovered concentrated slurry is compressed or thermally dried to remove the water contained therein and further compress the amount thereof. The slurry can be reused as a hydrofluoric acid source.

Claims

1. A wastewater treatment device is characterized by comprising:

a neutralizing mechanism for neutralizing the water to be treated mixed with the fluorine-containing material to be removed,

A means for adding a calcium component to the water to be treated to produce calcium fluoride,

A separation means for separating the removed matter containing the calcium fluoride from the water to be treated.

2. A wastewater treatment device is characterized by comprising:

a 1 st tank for storing the water to be treated mixed with the fluorine-containing material to be removed,

A neutralizing mechanism for adding an alkali source to the 1 st tank to neutralize the water to be treated,

A 2 nd tank for storing the water to be treated,

A mechanism for adding a calcium component to the 2 nd tank to produce calcium fluoride,

A 3 rd tank for storing the water to be treated containing the calcium fluoride,

And a separation mechanism for separating the removed material containing the calcium fluoride, which is stored in the 3 rd tank, from the water to be treated.

3. A discharged water treatment apparatus according to claim 1 or 2, wherein said neutralizing mechanism maintains pH of said water to be treated at 7 to 8.

4. The discharged water treatment apparatus according to claim 1 or 2, wherein the separation means is a filter device immersed in the water to be treated.

5. The discharged water treatment apparatus according to claim 4, wherein the water to be treated is filtered by a self-formed membrane formed on a surface of the filter device.

6. The discharged water treatment apparatus according to claim 1 or 2, further comprising a dewatering mechanism for dewatering the removed material separated from the treated water.

7. The discharged water treatment apparatus according to claim 1 or 2, further comprising a removing means for removing neutralized salts from the removed matter separated from the water to be treated.

8. The discharged water treatment apparatus according to claim 1 or 2, wherein the generation means adds calcium chloride to the water to be treated.

9. The drain water treatment apparatus according to claim 5, wherein the removed material obtained by periodically peeling off the self-formed film is added to the 2 nd tank.